The present invention relates to a method in the check weighing of a weighing system, in which method a hoist equipped with a weighing system is used to lift a load, which is weighed, and the value measured by the weighing system is recorded, and, in the method, the weighing system is adjusted as required, on the basis of the recorded values. The invention also relates to a software product and an arrangement in the check weighing of a weighing system, and to materials-handling equipment.
According to the prior art, in forestry and particularly in timber harvesting and timber trading, volume measurement has become an established form of measurement. This can indeed be done reliably, even automatically, for example using harvesters that are as such known and the measuring devices used in them. In addition, especially earlier, volume measurement has been performed, for example, at timber-processing plants, by, among other means, immersion, as well as by means of so-called circumference measurement or various measurement portals, such as a system based on laser measurement. However, particularly in terms of functioning logistics, it would be advantageous to have the measurement performed at the earliest possible stage in the timber-sourcing chain, such as most advantageously immediately in connection with the timber harvesting, or the local transportation of timber. Particularly during the harvesting of energy wood, which has become widespread in recent years, it is difficult to arrange reliable and functioning volume measurement in connection with a chipper that harvests the said timber grade or with some other harvester, because the timber material or timber grade being harvested is often of a small dimension and has a trunk shape that makes it practically impossible to accurately measure the diameter or length. In addition, in the case of energy wood, the form of harvesting generally used is so-called mass processing, instead of harvesting individual trees. This means principally that several trunks at a time are fed through the harvester head, possibly stripping them partially or totally, or alternatively completely without stripping them. For the aforementioned reasons among others, in forestry, particularly when trading in fibre and energy wood, and also in stumps harvested for energy use, a change has taken place to weighing the said timber grade already in the forest. In other words, a change has been made to using mass-based measurement instead of conventional volume-based measurement, because energy wood and other fractions collected from the forest have many different properties. For this purpose a special loader scale is fitted to the loader of a forwarder, by means of which each load lifted can be weighed. Typically, by summing the masses of the individual loads, the total mass of the forwarder's load can be determined and correspondingly by summing the masses of the loads the mass of the timber collected, by grade, from the entire harvesting area is calculated. Because generally the measurement performed using a loader scale in this way is the only weighing performed in the whole delivery chain, the weighing result must correspond with an acceptable accuracy to the real mass of the harvested and transported loads. The buyer and the seller can then be confident that the weighing will be correct. Part of the weighing system described above is a loader scale, which is fitted to the loader that acts as a hoist, especially in the case of a forwarder or timber truck. The hoist can be a crane, which is used to move any bulk or piece goods whatever, though the benefits of the solution according to the invention are emphasized in weighing systems, in which the particular characteristics of the material being weighed and of the actual loading process cause dispersion and imprecision in the weighing result.
Check weighing has been developed to evaluate and monitor the adjustment and operation of the loader scale and the weighing precision. Software, in which it is possible to program, for example, the acceptable accuracy, as well as other functions relating to the loader scale, is stored in the central unit belonging to the loader scale. A special test weight with a known mass is used in known check weighing, and is moved from the load space of the forwarder to a stack, according to normal working procedure, as is done normally with the loads handled in actual loading work. The moves are repeated and the value of each weighing is recorded. On the basis of the values given by check weighings made in this manner, the loader scale is adjusted so that the value measured/determined by the loader scale will correspond to the mass of the test weights used in the check weighing. The adjustment is preferably carried out by software, in such a way that the driver enters, or at least accepts the proposed correction, for example, through the central unit of the weighing system.
However, existing check weighing utilizing a special test weight with a known mass has certain drawbacks, particularly in a dynamic weighing situation. It has been shown in practical tests that, in certain cases, the real mass of the timber may deviate excessively from the mass obtained using loader scales. For example, by adjusting a loader scale to display precisely the mass of the test weight using a known check-weighing method, too great a mass may be obtained as the real result of the loader scale. There can be several reasons leading to this in the weighing system itself, in the material being weighed, or, for example, in the environmental conditions.
There is one significant difference between a test weight and real loads, particularly energy-wood loads. An energy-wood load, with a weight of an order of magnitude corresponding essentially to that of the test weight, has a length that is typically considerably longer than that of the test weight. Such a load can have a nearly arbitrary shape in its other dimensions, which can cause variations in a precise weighing performed in a dynamic weighing situation, in which the load is in a rotational and/or translational movement relative to one or more axes. At its longest, an energy-wood load can be as much as nearly ten-meters long, comprising entire energy trees, or at least long parts of their trunks. Generally, the goods grade, mass, and dimensions of the load affect the loading event, and thus the measurement result. Other influencing factors include the environment, the driver, and the machine, such as the forwarder. In other words, there can be several different reasons for a loader scale to show an erroneous load, compared to the real mass.
In addition, test weighing using a special test weight, along with its repeats, takes up an excessively large part of actual working time and is not productive. Therefore in practice test weighing may be performed only about once a week, which is not necessarily sufficient to ensure sufficiently good weighing precision. Conditions and the operation of the device may, however, change during a week, leading to an increased risk of a weighing error. Typically such a change can be, for example, a change in the electronics effecting the measurement of the shackle, or especially in the zero position or angular coefficient of the strain gauges, which may indicate a need to perform calibration or check weighing. Similarly, for example, over the course of a week or a day the timber grade and also the operator of the weighing system and loader may change, which can also increase the error. In addition, check weighing always demands a separate test weight, which must be carried along with the forwarder. The test weight may be lost, or damaged when being handled, or its other properties may change, despite it being built to be as stable and durable as possible for its purpose, which will in turn act to weaken the reliability of the check weighing.